JP2003077646A - Induction heater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an induction heater which can considerably increase the temperature uniformity of a heating unit. SOLUTION: In the induction heater having an oblong first exciting coil and using an AC power source for supplying induction current for heating to the exciting coil, a second exciting coil is disposed on both ends of a magnetic flux generation passage of the first exciting coil, a resonance circuit with a resonance capacitor connected in parallel to the second exciting coil is constituted, and connected to the AC power source by an opening/closing means connected in series to the second exciting coil.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction heating device for fixing heat-meltable powder such as toner on paper.

[0002]

2. Description of the Related Art Various methods and heating coil shapes for heating a planar object using induction heating have been devised. In such a case, the planar heating coil shape as shown in FIG. 6 exhibits a relatively high heating efficiency because the area of the heating coil facing the object to be heated can be wide. Note that FIG. 7 is shown in FIG.
FIG. 3B is an AA ”cross-section heat generation distribution diagram.

[0003]

By using such a coil shape, as shown in FIG. 7, the central portion of the heating coil has a relatively uniform heat generation distribution. In many cases, the heat generation was abnormal because it was not uniform, and the heat generation escaped to the outside because it hits both ends of the heating portion.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an induction heating device capable of significantly improving the temperature uniformity of a heat generating portion.

[0005]

In order to achieve the above-mentioned object, the present invention has an elliptical first exciting coil, and an induction using an AC power supply for supplying an induction current for heating to the exciting coil. In the heating device, second exciting coils are arranged at both ends of the first exciting coil magnetic flux generation path, and a resonance circuit is formed by connecting a resonance capacitor in parallel to the second exciting coil to form a resonance circuit. The exciter coil is connected to the AC power source by an opening / closing means connected in series.

Further, the present invention provides an induction heating apparatus using an AC power supply which has an elliptical first exciting coil and supplies a heating induction current to the exciting coil. Second and third exciting coils are arranged at both ends of the generation path, and the second and third exciting coils are respectively connected in parallel to form a second resonance circuit in which resonance capacitors are connected in parallel. An opening / closing means connected in series to the second and third exciting coils is provided, and the AC power source is connected to the second and third exciting coils in accordance with a signal for energizing the first exciting coil. It is characterized by

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a basic configuration diagram of an induction heating apparatus according to the present invention. In FIG. 1, L1 is a main induction heating coil for inducing an induction current in a heating object made of a planar magnetic material, and C2 is the above-mentioned. The main induction heating coil L1 is a resonance element, and L2 and L3 are auxiliary induction heating coils for correcting the temperature distribution of the main induction heating coil L1. The series inductance of the auxiliary induction heating coils L2 and L3 and the resonance element C3 are used. It has a resonance element independent of the resonance element of the main heating system.

In the present invention, L1 and C2, L2 and L3,
It is desirable to set the relationship of C3 to L1 · C2≈ (L2 + L3) · C3.

D1 to D4, NF1 and C1 are rectifying circuits for rectifying AC power and converting it into pulsating current. The pulsating current is supplied to the heating coil according to switching of TR1 which is a power switch element, and The TR1 has an IC1 for controlling its switching state connected to a control terminal,
FIG. 4 is a power conversion circuit block diagram in which D5 that rectifies the flywheel current from the heating coil when the switch is turned off is connected in anti-parallel, and constitutes a power supply circuit for supplying heating power to the heating coil. .

Reference numerals 7 and TH1 are measuring circuits for detecting the temperature at the center of the heating portion, 8 and TH2 are end temperature measuring circuits for detecting the temperature at the end portions of the heating portion, and 9 is the temperature and end portion of the heating portion central portion. The switch element of SW1 which detects the difference of the heat generation temperatures of the parts and determines whether or not to apply the AC power to the auxiliary heating coils L2 and L3 is controlled according to the temperature difference.

FIG. 2 is a top perspective view of the heating coil of the present invention seen from above, and the main heating coil 1 has an elongated shape in order to efficiently heat a planar object to be heated.
Then, auxiliary heating coils 2 and 3 are arranged at positions overlapping the main heating coil winding prayer point.

Next, the operation will be described.

When a heating command signal is sent to the induction heating power source, a frequency of 20 is output to the output terminal of the induction heating power source.
High frequency AC power of about kHz to 100 kHz is generated. This AC power is applied to the main heating coil 1, and the main heating coil 1 generates an AC magnetic field. At this time, the AC power applied to the main heating coil 1 varies depending on the object to be heated, but is usually about 200 to 300 W to several kW.

The AC magnetic field generated by the AC power applied to the heating coil 1 generates an eddy current in the object to be heated. The eddy current causes Joule heat to be generated in the object to be heated, so that the object to be heated itself generates heat. This electromagnetic induction action causes the object to be heated to generate heat, and the temperature of the object to be heated rises.

Here, the temperature detection circuit 7 including the temperature measuring element TH1 for measuring the temperature of the object to be heated monitors the temperature rise of the object to be heated at any time, and the temperature detected at the central portion of the object to be heated is supplied to the induction heating power source. To be fed back. The induction heating power source compares the set target temperature with the detected temperature, and when the detected temperature approaches the set target temperature, the heating target is controlled by using a proportional control or the like, or a control method commonly called PID control. Keep the temperature near the center of the object constant.

Then, the temperature detecting circuit 8 of the temperature measuring element TH2 for measuring the end temperature of the object to be heated monitors the end temperature rise of the object to be heated at any time and measures the temperature of the central part of the object to be heated. By inputting the temperature measurement outputs of the temperature measurement element TH1 and the temperature detection circuit 7 to the temperature difference detection circuit 9, the switch element SW1 is operated according to the temperature difference between the central portion and both ends of the heating target.
Open and close.

Auxiliary heating coils L2 and L3 of the high frequency heating power generated by the induction heating power source are connected by the switching element SW1 to the resonance circuit composed of L2, L3 and C3.
The temperature of the induction heating coil as a whole is corrected by controlling the application to the auxiliary heating coil. By adopting such a configuration, at the time of heating start-up, the heat generated at both ends is more likely to escape than the central part of the heating coil, but as shown in the heating coil heat distribution of FIG. 3, the auxiliary heating coils L2 and L3 are also By supplying power at the same time, the heat distribution of the auxiliary coils L2 and L3 is applied to both ends in accordance with the heat distribution of the main heating coil, so that the amount of heat escaping from the ends is compensated for and the heating shown by the broken line in FIG. It is possible to generate heat uniformly over the entire area of the coil.

Further, in the case of steady heat generation, the central portion is relatively easily deprived of heat, whereas the opposite end portions are less likely to be deprived of heat as opposed to the start-up, so the temperature distribution is low in the central portion and both ends are low. The temperature of the end temperature detection TH2 is higher than the measured temperature of the central temperature detection TH1 at this time.
Since the auxiliary heating coils L2 and L3 are not energized by opening the switch element SW1 in the temperature difference detection control circuit 9, the heat generation amount at both ends is reduced with respect to the central portion of the heating coil, and the heat generation distribution of the object to be heated is reduced. Can be made uniform over the entire length of the coil.

FIG. 5 is a diagram showing another embodiment of the present invention. In the system shown, auxiliary heating coils L2 and L3 can be simply constructed as compared with FIGS.

In the present embodiment, the central heating coil L1
Is similar to that of FIG. 1, but the auxiliary heating coils L2 and L3 are independently configured. Therefore, there is no need to adopt a complicated coil configuration such as winding two coils in series as shown in FIG. 2, and there is a feature that the production of the auxiliary heating coil becomes very simple. Specifically, as shown in FIG. 5, L2 and L3 are independently configured with respect to L1 to form L2.
And L3 are connected in parallel, and the capacitance element of C3 is connected to the combined inductance thereof to have a resonance element independent of the resonance element of the main heating system.

In the present embodiment, it is desirable that the relationship between L1 and C2, L2 and L3, and C3 be L1.C2.apprxeq. (L2 / L3) .C3.

The operation is similar to that of FIG. 1, but by adopting such an auxiliary coil structure, L2 and L
Since 3 can be the same one, there is also an advantage that it is suitable for mass production.

[0024]

As is apparent from the above description, according to the present invention, the induction using the AC power supply having the first elliptical excitation coil and supplying the induction current for heating to the excitation coil. In the heating device, second exciting coils are arranged at both ends of the first exciting coil magnetic flux generation path, and a resonance circuit is formed by connecting a resonance capacitor in parallel to the second exciting coil to form a resonance circuit. Since the connecting means is connected to the AC power supply by the opening / closing means connected in series to the exciting coil, the temperature uniformity of the heat generating portion can be significantly improved.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an induction heating device according to the present invention.

FIG. 2 is a perspective view of an induction heating coil of the induction heating device according to the present invention as seen from the front.

FIG. 3 is a heat generation distribution diagram of AA ″ cross section of FIG. 2;

FIG. 4 is a sectional view of an induction heating device according to the present invention.

FIG. 5 is a configuration diagram of an induction heating device showing another embodiment of the present invention.

FIG. 6 is a configuration diagram of a conventional heating coil.

FIG. 7 is a heat generation distribution diagram of AA ″ cross section of FIG. 6;

[Explanation of symbols]

7,8 Temperature detection circuit 9 Temperature difference detection control circuit L1 main induction heating coil L2, L3 auxiliary induction heating coil C2 Main coil resonance capacitor C3 Auxiliary coil resonance capacitor TR1 main power switch element SW1 switch element TH1, TH2 Temperature detection element

Claims (2)

[Claims] 1. An induction heating apparatus using an AC power supply having an elliptical first exciting coil and supplying a heating induced current to the exciting coil, wherein both ends of the first exciting coil magnetic flux generation path are provided. A second exciting coil is arranged in the section, and a resonance circuit is formed by connecting a resonance capacitor in parallel to the second exciting coil, and the opening and closing means connected in series to the second exciting coil forms the resonance circuit. An induction heating device characterized by being connected to an AC power supply. 2. An induction heating apparatus using an AC power supply which has an elliptical first exciting coil and supplies a heating induction current to the exciting coil, wherein each of the first exciting coil magnetic flux generation paths is provided. The second and third exciting coils are arranged at both ends, the second and third exciting coils are connected in parallel, and the second resonant circuit is formed by connecting the resonant capacitors in parallel. An opening / closing means connected in series to the three exciting coils is provided, and
The second and the third according to a signal to be applied to the exciting coil of
An induction heating device characterized in that the AC power supply is connected to the exciting coil of.